Mix Examples-Human Reproduction Questions in English

(D) Natural parthenogenesis is a phenomenon where an unfertilized egg develops into a complete individual.
In $Apis$ $mellifera$ (Honey Bee),the queen lays unfertilized eggs that develop into haploid males,known as drones,through the process of arrhenotoky (a type of parthenogenesis).
Therefore,honey bees are a classic example of natural parthenogenesis.

(A) Menopause is the permanent cessation of the primary functions of the ovaries in the female reproductive system.
Due to the decline in the production of ovarian hormones like estrogen and progesterone,the negative feedback mechanism on the anterior pituitary gland is reduced.
As a result,the anterior pituitary gland secretes higher levels of gonadotropins,specifically Follicle-Stimulating Hormone $(FSH)$ and Luteinizing Hormone $(LH)$,in an attempt to stimulate the ovaries.
These elevated levels of gonadotropins in the blood lead to an increased excretion of these hormones in the urine.
Among the given options,$FSH$ is the primary hormone that shows a significant rise in urinary excretion during menopause.

(C) The hormone $Luteotrophin$,also known as $Prolactin$ $(PRL)$,is secreted by the anterior pituitary gland.
It plays a crucial role in the development of mammary glands and the stimulation of milk production (lactation).
Furthermore,in certain species,$Prolactin$ is known to maintain the secretory activity of the $corpus$ $luteum$,thereby supporting the production of $progesterone$.

(A) is correct because $Leydig$ cells (interstitial cells) in the testes are stimulated by $LH$ to synthesize and secrete androgens,primarily $testosterone$.
$B$ is incorrect because while $progesterone$ is secreted by the $corpus$ $luteum$,the hormone responsible for softening ligaments during childbirth is $relaxin$.
$C$ is incorrect because $estrogen$ is primarily secreted by the growing ovarian follicles,not $Sertoli$ cells.
$D$ is incorrect because $progesterone$ is a steroid hormone and is chemically identical regardless of whether it is produced by the $corpus$ $luteum$ or the $placenta$.

(B) The correct answer is $B$. Gynaecomastia is a condition characterized by the enlargement of breast tissue in males. This often occurs due to a hormonal imbalance,specifically an increase in estrogen levels or a decrease in testosterone levels,which can lead to the development of mammary glands similar to those in females.

(D) Estrogen is a primary female sex hormone responsible for the development and maintenance of secondary sexual characteristics.
$1$. It promotes the growth and development of the female reproductive tract,including the fallopian tubes,uterus,and vagina.
$2$. It stimulates the development of the mammary glands,specifically the growth of the duct system within the breasts.
$3$. It contributes to the enlargement and maturation of the female external genitalia.
Therefore,all the listed effects are caused by the secretion of large quantities of estrogen.

(A) The $Corpus$ $luteum$ is a temporary endocrine structure in female ovaries that is involved in the production of relatively high levels of progesterone and moderate amounts of estradiol and inhibin $A$.
It is formed from the ruptured follicle after ovulation.
This structure is characteristic of mammals (such as $Rat$, $Rabbit$, and $Man$).
In amphibians like the $Frog$, the follicle does not form a $Corpus$ $luteum$ after ovulation.
Therefore, the correct answer is $Frog$.

(D) Semen is a milky,viscous,and alkaline fluid.
The quantity of semen is $2.5$ to $4.0 \ ml$ per ejaculation,containing approximately $400$ million sperms.
The fluid component (seminal plasma) is secreted by the accessory glands,which include the epididymis,seminal vesicles,prostate gland,and bulbo-urethral (Cowper's) glands.
Therefore,all the listed options contribute to the composition of semen.

(D) Ejaculation is the process of discharging semen from the male reproductive tract.
$1$. It involves rhythmic contractions of the bulbospongiosus and ischiocavernosus muscles,which are striated muscles.
$2$. The process is regulated by the sympathetic nervous system,which triggers the contraction of the vas deferens,seminal vesicles,and prostate gland.
$3$. It is physiologically associated with the sensation of orgasm in males.
Therefore,all the given statements are correct.

(A) The vaginal environment is acidic,which is hostile to sperm survival and motility. Upon ejaculation into the vagina,the acidic pH (typically $3.8$ to $4.5$) causes the sperms to lose their motility relatively quickly. Research indicates that sperms typically become non-motile within $60$ minutes of being deposited in the vagina.

(D) The correct answer is $D$.
In rabbits,ovulation does not occur spontaneously in the absence of mating.
Instead,the act of copulation provides the necessary neural stimulus to the hypothalamus,which triggers the release of gonadotropins from the anterior pituitary gland.
This surge of hormones leads to the rupture of the ovarian follicles and the release of the egg.
Therefore,rabbits are classified as induced ovulators.

(A) Ovulation is the process of releasing a secondary oocyte from the ovary. It can be detected by several physiological changes:
$1$. Basal body temperature $(BBT)$ rises by approximately $0.5^{\circ}F$ to $1.0^{\circ}F$ after ovulation due to the thermogenic effect of progesterone.
$2$. The cervical mucus becomes thin, clear, and stretchy (spinnbarkeit), and when dried on a slide, it exhibits a characteristic 'fern pattern' due to high estrogen levels.
$3$. Urinary excretion of estrogen metabolites (like estradiol) increases significantly just before ovulation.
Since options $A$, $B$, and $C$ are all valid indicators, in a single-choice context, the rise in $BBT$ is a classic clinical indicator.

(D) At the onset of puberty,females undergo several physiological and anatomical changes known as secondary sexual characters. These include:
$1$. The enlargement of breasts (thelarche).
$2$. The beginning of the menstrual cycle (menarche).
$3$. The cessation of rapid growth in long bones,leading to the stabilization of height.
Therefore,all the mentioned options are correct.

(A) The prepubertal period is the phase of development that occurs before the onset of puberty. During this stage,the body undergoes significant growth and the enlargement of various organ systems. Furthermore,it involves the gradual maturation of reproductive mechanisms,preparing the individual for the physiological changes that will occur during puberty.

(C) Ovulation is the process in which a mature ovarian follicle ruptures and releases an egg (ovum).
This process occurs in the ovary.
In a typical $28$-day menstrual cycle,ovulation occurs at approximately the $14^{th}$ day of the cycle,triggered by the $LH$ surge.
Therefore,both the location (ovary) and the timing (about the $14^{th}$ day) are correct.

(B) The correct matches are as follows:
$(a)$ Hyaluronidase is an enzyme found in the acrosome of the sperm,which helps in the acrosomal reaction to penetrate the egg layers.
$(b)$ Corpus luteum is the structure formed after ovulation that secretes progesterone.
$(c)$ Gastrulation is the process involving extensive cell migration and morphogenetic movements to form the three germ layers.
$(d)$ Capacitation is the physiological maturation process of sperm in the female reproductive tract,leading to sperm activation.
$(e)$ Colostrum is the antibody-rich milk produced by the mammary glands during the initial days of lactation.
Therefore,the correct combination is $(a)-(i), (b)-(iii), (c)-(ii), (d)-(v), (e)-(iv)$.

(C) Ejaculation is the forceful expulsion of semen from the urethra during sexual intercourse.
Spermatogenesis is the process of formation of spermatozoa.
Spermiogenesis is the transformation of spermatids into spermatozoa.
Insemination is the process of transferring semen into the female reproductive tract.

(C) Female rabbits are classified as $Polyestrus$ animals. This means they experience multiple estrous cycles throughout their breeding season. Unlike $Monoestrus$ animals that have only one cycle per year,or $Diestrus$ animals that have two,rabbits can undergo several cycles,allowing them to breed multiple times during the year.

(A) freshly laid,unfertilized egg of a hen is a single cell. The yolk of the egg represents the female gamete (ovum) along with stored nutrients,and it is enclosed within the vitelline membrane. Even though it is large in size,it remains a single cell until fertilization and subsequent cleavage occur.

(A) The eggs of eutherian mammals,such as rabbits and humans,are classified as $Alecithal$ or $Microlecithal$.
These eggs contain a very small or negligible amount of yolk because the developing embryo receives nutrition directly from the mother through the placenta.
Therefore,the correct option is $A$.

(D) Elephant is a placental mammal.
In placental mammals,the egg contains a very small amount of yolk,which is termed as $Microlecithal$.
Furthermore,the yolk is distributed evenly throughout the cytoplasm,which is termed as $Isolecithal$ or $Homolecithal$.
Therefore,the eggs of an elephant are $Microlecithal$ and $Isolecithal$.

(C) In $Mosaic$ eggs,the developmental fate of each blastomere is predetermined at a very early stage. If a part of the embryo is removed,the remaining parts cannot compensate for the loss,leading to a defective embryo. This is because the cytoplasm of the blastomeres differentiates early in development with reference to the tissues of the adult organism.

(A) The calcareous shell present around the eggs of birds is porous.
This porous nature allows for the gaseous exchange required for the developing embryo.
Specifically,it facilitates the diffusion of oxygen $(O_2)$ into the egg and carbon dioxide $(CO_2)$ out of the egg.
Therefore,the shell and shell membranes are permeable to $O_2$ and $CO_2$.

(B) The classification of eggs based on the amount of yolk is as follows:
$1$. $Alecithal$: Eggs with no yolk (e.g.,placental mammals).
$2$. $Microlecithal$ (or $Oligolecithal$): Eggs with a very small amount of yolk (e.g.,$Hydra$,sea urchin,$Amphioxus$,marsupials,and eutherians).
$3$. $Mesolecithal$: Eggs with a moderate amount of yolk (e.g.,amphibians).
$4$. $Polylecithal$ (or $Macrolecithal$): Eggs with a large amount of yolk (e.g.,birds and reptiles).
Therefore,eggs containing a very small amount of yolk are called $Microlecithal$ eggs.

(B) Mammals are $Viviparous$ (except monotremes),meaning the embryo develops inside the mother's body. Because the developing embryo receives nutrition directly from the mother through the placenta,there is no need for a large amount of yolk in the egg. Consequently,mammalian eggs contain a very small amount of yolk $(microlecithal)$ which is evenly distributed throughout the cytoplasm $(isolecithal)$.

(C) When nuclei from an $8$-celled stage embryo are transplanted into enucleated eggs (a process known as nuclear transplantation or cloning),the recipient egg often initiates development.
However,because the donor nuclei from an $8$-celled stage have already undergone some degree of differentiation and epigenetic modification,they are generally unable to support full development to a viable organism.
Consequently,while the egg may begin to divide (cleavage),the process is typically arrested after a certain period,leading to the failure of the embryo to develop further.

(B) Precocious puberty refers to the onset of secondary sexual characteristics at an age significantly earlier than the normal range for puberty (typically before age $8$ in girls and before age $9$ in boys).
It involves the premature activation of the hypothalamic-pituitary-gonadal axis,leading to early physical maturation.

(A) The corpus luteum is formed from the ruptured Graafian follicle after ovulation under the influence of the Luteinizing Hormone $(LH)$.
Once formed,the corpus luteum secretes large amounts of progesterone,which is essential for maintaining the endometrium.
Therefore,the secretion of progesterone by the corpus luteum is initiated and maintained by $LH$.

(C) Sperms are generally sensitive to the $pH$ of their environment.
Acidic $pH$ is harmful to sperms,as it kills them or significantly reduces their motility and activity.
Conversely,a slightly alkaline or higher $pH$ (within a physiological range) is favorable for sperm motility and survival.
Therefore,in a higher $pH$ environment,sperms become highly active and exhibit a longer lifespan compared to an acidic environment.

(A) In centrolecithal eggs,such as those found in insects,the yolk is concentrated in the center of the egg. During superficial cleavage,the nuclei divide repeatedly without cytoplasmic division,and these nuclei migrate to the periphery. Subsequently,the cytoplasm surrounds each nucleus to form cells. As a result,a layer of cells is formed around the central mass of yolk. Therefore,the yolk is surrounded by the cells.

(D) Fraternal twins,also known as dizygotic twins,are produced when two separate eggs are released from the ovaries and are fertilized by two separate sperms simultaneously. This results in two distinct zygotes,each with its own unique genetic makeup,which then develop into two separate individuals.

(D) The correct answer is $(D)$. Dizygotic twins are also known as fraternal twins. They are formed when two different ova are fertilized by two different sperms simultaneously in the same reproductive cycle. Since they arise from two different zygotes,they are genetically distinct.

(D) In a mammal,most body cells are diploid $(2n = 40)$. The seminiferous tubules contain various types of cells:
$1$. Spermatogonia (diploid,$2n = 40$) which undergo mitosis.
$2$. Primary spermatocytes (diploid,$2n = 40$) which undergo meiosis $I$.
$3$. Secondary spermatocytes (haploid,$n = 20$) which undergo meiosis $II$.
$4$. Spermatids and spermatozoa (haploid,$n = 20$).
Since the seminiferous tubule contains both diploid cells (spermatogonia and primary spermatocytes) and haploid cells (secondary spermatocytes,spermatids,and sperms),some cells will have $40$ chromosomes and others will have $20$ chromosomes.

(A) In $Centrolecithal$ eggs,the yolk is concentrated in the center of the egg,while the cytoplasm is distributed in the peripheral layer surrounding the yolk. This type of egg is commonly found in insects.

(A) Macrolecithal (or megalecithal) eggs are those that contain a large amount of yolk.
These eggs are characteristic of organisms where the embryo requires significant nutrients for development before hatching.
Birds and reptiles lay macrolecithal eggs because their embryos develop outside the mother's body and rely entirely on the yolk for sustenance.
Therefore,the correct answer is Birds and Reptiles.

(B) In a human female, the reproductive phase typically begins at menarche (around $12-13$ years of age) and ends at menopause (around $45-50$ years of age).
During each menstrual cycle, usually one ovum is released from the ovaries.
The total reproductive span is approximately $35-40$ years.
Calculating the number of cycles: $35 \text{ years} \times 12 \text{ months/year} = 420$ cycles.
Therefore, approximately $400$ ova are released throughout the reproductive life of a human female.

(A) The correct pair is $A$.
After ovulation,the ruptured Graafian follicle transforms into a temporary endocrine structure called the corpus luteum.
Option $B$ is incorrect because sebum is an oily secretion,not salt.
Option $C$ is incorrect because the $SA$ node is the pacemaker,while the Bundle of His is part of the conducting system of the heart.
Option $D$ is incorrect because Vitamin $B_7$ is Biotin,whereas Niacin is Vitamin $B_3$.

(D) The eggs of birds are classified based on the amount and distribution of yolk.
$1$. They contain a very large amount of yolk, which is why they are called $Megalecithal$ or $Macrolecithal$.
$2$. Due to the high yolk content, they are also referred to as $Polylecithal$.
$3$. Since all these terms describe the same characteristic of bird eggs, the correct answer is $All \, of \, the \, above$.

(C) Holoblastic cleavage refers to the complete division of the egg into blastomeres. This occurs in eggs with little or no yolk (isolecithal) or moderate amounts of yolk (mesolecithal).
$1$. $Hydra$ (Cnidarian) undergoes holoblastic cleavage.
$2$. $Amphioxus$ (Cephalochordate) undergoes holoblastic cleavage.
$3$. $Frog$ (Amphibian) undergoes holoblastic cleavage.
$4$. $Hen$ (Bird) has telolecithal eggs with a large amount of yolk,which restricts cleavage to a small disc on the surface (meroblastic cleavage).
Since the question asks for an example of holoblastic cleavage,and $Hydra$,$Amphioxus$,and $Frog$ all exhibit this,the question is likely referring to a specific context or may have multiple correct answers. However,in many standard textbooks,$Frog$ is the classic example used to illustrate holoblastic cleavage.

(A) Megalecithal or macrolecithal eggs are those that contain a very large amount of yolk.
This type of egg is characteristic of organisms that require significant energy reserves for embryonic development before hatching.
Reptiles and birds (Aves) produce megalecithal eggs to support the development of the embryo outside the mother's body.
Monotremes (egg-laying mammals) also produce megalecithal eggs.
Therefore,the correct group containing megalecithal eggs is reptiles,birds,and monotremes.

(B) Mammals are primarily viviparous,meaning they give birth to live young.
Because the developing embryo receives nutrition directly from the mother through the placenta,there is no need for a large amount of yolk in the egg.
Consequently,mammalian eggs are microlecithal (containing a very small amount of yolk) and alecithal (virtually yolkless).

(A) The classification of eggs is based on the amount and distribution of yolk:
$1$. Centrolecithal eggs have yolk concentrated in the center,which is characteristic of insects.
$2$. Macrolecithal (or Megalecithal) eggs contain a large amount of yolk,found in birds and reptiles.
$3$. Microlecithal eggs contain a small amount of yolk,found in eutherian mammals.
$4$. Alecithal eggs contain almost no yolk,found in eutherian mammals (though often classified as microlecithal due to trace amounts).
Therefore,the pair $A$ (Centrolecithal egg - Insect) is correct.

(D) The pitch of the voice is determined by the frequency of vibration of the vocal cords.
In females,the vocal cords are generally shorter and thinner,which allows them to vibrate at a higher frequency.
This higher frequency of vibration results in a higher-pitched voice compared to adult males,whose vocal cords are longer and thicker,resulting in a deeper,lower-pitched voice.

(B) Polyoestrous mammals are those that experience multiple oestrous cycles throughout the year or during their breeding season.
$1$. Humans and monkeys are primates that exhibit a menstrual cycle,not an oestrous cycle.
$2$. Cats are polyoestrous mammals,meaning they can go into heat multiple times during their breeding season.
Therefore,the correct answer is $B$.

(D) In human reproductive biology,reproductive organs are classified into primary and secondary sex organs.
Primary sex organs are the gonads (testes in males and ovaries in females),which produce gametes and secrete sex hormones.
Secondary sex organs are the ducts,glands,and external genitalia that facilitate the transport of gametes and support the reproductive process.
$A$,$B$,and $C$ (Vagina,Penis,and Prostate) are all secondary sex organs involved in the transport or support of gametes.
The mammary glands are considered accessory reproductive organs or secondary sexual characteristics,but they are not classified as secondary reproductive organs in the same functional category as the ducts and glands of the reproductive tract. However,in the context of standard biology questions,the mammary glands are often distinguished from the primary reproductive tract components.

(C) Secondary sexual characteristics in females are triggered by the secretion of estrogens. These include the development of mammary glands $(A)$,the appearance of pubic and axillary hair $(B)$,and the onset of the menstrual cycle $(D)$. $A$ low-pitched voice is a secondary sexual characteristic in males,caused by the effect of androgens on the larynx. Therefore,a low-pitched voice is $NOT$ a secondary sexual characteristic in females.

(D) Homologous organs are those that share a common embryonic origin but may perform different functions.
$1$. Clitoris and Penis are homologous as they develop from the same genital tubercle.
$2$. Vagina and Prostatic Utricle are homologous structures.
$3$. Uterus and Prostatic Utricle are also considered homologous.
$4$. Oviduct (Fallopian tube) and Prostate are not homologous. The Oviduct develops from the Mullerian duct,whereas the Prostate develops from the urogenital sinus. Therefore,option $D$ is the incorrect pair.

(D) Pseudopregnancy (also known as false pregnancy) is a condition where an individual exhibits signs and symptoms of pregnancy without the presence of a fetus.
In many mammals,this occurs due to the persistence of the corpus luteum after ovulation in the absence of fertilization.
The corpus luteum continues to secrete progesterone,which maintains the uterine lining and mimics the hormonal state of pregnancy.
Therefore,hormonal imbalance and the absence of fertilization after ovulation are key factors contributing to this condition.

(C) The reproductive cycle in female mammals is divided into two types based on the physiological changes occurring in the reproductive tract:
$1$. $Oestrus$ cycle: This is observed in non-primate mammals such as cows,sheep,rats,deer,dogs,and tigers.
$2$. Menstrual cycle: This is observed in primates such as monkeys,apes,and humans.
Therefore,the $Oestrus$ cycle is a characteristic of non-primate mammalian females.

(A) $Freemartin$ is a sterile female calf that is born as a twin to a male calf. This occurs in cattle when the placentas of the twin fetuses fuse,allowing the exchange of blood and hormones between them. The male hormones (androgens) from the male fetus reach the female fetus and interfere with the development of her reproductive system,resulting in a sterile female. The male twin remains normal.